1

High Institute for Engineering & Technology, AL-Obour Electrical Eng. Dept, 4

th Year, Electronics & Comm. Section

Course Title : Electronics for Instrumentations ELC (426) Sheet 3

Dr. Eng. Ibrahim F.Tarrad :Instructor

Eng. Saad EL-Sayed

Problem 3.1: For the Schmitt trigger circuit shown below, if R1 = 10 K, then R2 = 60K, R3 = 10K, VCC = 12Vand the diodes are assumed to have a constant 0.7V drop when conducting (VD = 0.7V) do the following:

a. Derive an expression and calculate the Lower and Upper Threshold Point voltage (VLTP and V UTP) then draw the voltage transfer characteristics.

b. Calculate and draw the output waveform for the output if the input voltage V1 is given by: V1 = 5 sin t.

c. Show how to limit the output voltage amplitude, VO to be 5V.

vo

R1

-

+

R2

vin

D1 D2

R3

Problem 3.2: The square and triangular wave generator circuit of the following figure, if R1 = 1 K, R2 = 3K, R3 = 0.5 K, R = 2 K, C = 10 nF, VZ = 4.3 V and supply voltage, VCC = 9 V.

For this circuit do the following:

a. Derive an expression for the frequency of oscillation, f. b. Sketch the output waveforms VO1 and VO2 indicating the voltage levels and the

essential times.

c. Determine the current passing through the Zener diodes, iZ.

vo1

R1

-

+

R2

R3-

+

R

C

Z1

Z2

vo2

2

Problem 3.3: For the circuit shown in figure, if R1 = 1 K, Rp = 5K, R2 = 1K, R = 2.2 K and C = 100 nF. Calculate:

a. Maximum frequency. b. Minimum frequency. c. Duty cycle in both above cases.

vo

R

-

+

R2

Rp

Z1

Z2

R1

C